The subject invention relates to a process and apparatus for supplying a release agent, and in particular to use of the process and apparatus in the manufacture of oriented strand board and other ligno-cellulosic composite materials.
Ligno-cellulosic composite materials are commonly prepared by hot pressing a mat formed from multiple layers of wood xe2x80x9cflakesxe2x80x9d or xe2x80x9cstrands,xe2x80x9d coated with a binding material such as phenol formaldehyde resin or isocyanate resin, together with a wax, to form a composite panel. The hot press is typically characterized by two steel press plates that compress the mat at a predetermined temperature and pressure. Examples for the fabrication of ligno-cellulosic composites are described in U.S. Pat. No. 5,525,394 to Clarke et al., and U.S. Pat. No. 5,635,248 to Hsu et al., the complete contents of each is herein incorporated by reference.
Organic polyisocyanates, such as methylene diphenyl diisocyanate (MDI) are known to be superior binders for use with ligno-cellulosic material, due to the superior strength and adhesion properties these binders impart on the composite panel. However, ligno-cellulosic strands coated with organic polyisocyante binders tend to stick to the metal surface of the press plates when the mat is pressed. Often the final product is damaged during removal of the mat from the press and significant time is required to remove the ligno-cellulosic material from the surfaces of the press plates.
To avoid such adhesion problems, other binding agents, such as phenol formaldehyde, are often used on the faces of the boards to be produced. These binding agents generally diminish the adherence of the coated ligno-cellulosic material to the surfaces of the press plates. Another solution to the binding problem is to face the ligno-cellulosic material with paper. Unfortunately, these options increase the complexity and cost of the manufacturing process.
Attempts to solve the adhesion problems that occur with organic polyisocyante binders has tended to focus on the use of release agents such as oils, wax polishes, metallic soaps, silicones and polytetrafluoroethylene. These agents may be used internally, i.e., as an emulsion or mixture with the organic polyisocyanate, or externally, i.e., applied to the metal surfaces of the press plates, to the ligno-cellulosic material itself or to the belts underneath and/or above the ligno-cellulosic material which guide the mat into the press plates. In general, these release agents, and their method of application, have not demonstrated significant improvement in release properties or have proven to be too expensive or detrimental to the physical properties of the resulting product. For example, many external release agents, such as metallic soaps, will cause discoloration of the ligno-cellulosic product or evaporate off of the surface to which they are applied, prior to entering the pressing operation. In addition, external wax release agents, particularly petroleum derived wax release agents, tend to coat and xe2x80x9cgum-upxe2x80x9d the moving parts of the machinery. Specifically, the high temperatures at which the press platens operate cause these agents to caramelize.
Thus, there is a need in the wood product manufacturing industry for a process and apparatus for efficiently applying a release agent to provide a means for producing ligno-cellulosic composite made exclusively with an organic polyisocyante binder, while eliminating adhesion of the coated wood strands to the press plates. Further, there is a need for a means to economically apply such a release agent, while avoiding the discoloration of the final ligno-cellulosic product and adhering of the releasing agent to the moving parts of the wood product manufacturing equipment.
In summary, the invention includes apparatus for distributing a soap based release agent, preferably a metallic soap, upon a surface comprising; a means for metering a controlled quantity of a liquid metallic soap into a pressurized water stream to form a pressurized aqueous solution having a controlled dilution ratio of soap to water, at least one manifold connected to receive the pressurized aqueous solution, and a plurality of nozzles mounted upon the manifold to uniformly distribute the pressurized liquid solution upon at least one surface. The surface may further be defined as a planar surface, moving unidirectional along a fixed path at a predetermined variable speed and defined by a surface area of length multiplied by width. The planar surface has a fixed width, wherein the surface area moving past a fixed point for a predetermined period of time is a function of the speed of the planar surface moving past the fixed point. Preferably, the apparatus further comprises at least one regulating means for regulating the dilution ratio of the soap to water. The dilution ratio is controlled by regulating the quantity of the metallic soap metered into the pressurized water stream. This quantity of metallic soap is correlative with the speed of the planar surface, so as to maintain a relatively constant measure of metallic soap per unit of surface area as the speed of the planar surface is varied. Thus, the dilution ratio is adjusted to maintain a relatively constant measure of metallic soap per square foot of surface area during increases or decreases in surface speed.
The invention, by way of summary, also includes apparatus for manufacturing orientated strand board comprising:
(1) a means for coating wood strands with at least one organic polyisocyanate binder,
(2) a means for forming a mat of said coated wood strands,
(3) a device for distributing a release agent upon said mat and a conveyer belt used to transport said mat, said device comprising;
(a) a means for metering a controlled quantity of a soap based release agent into a pressurized water stream to form a pressurized aqueous solution having a controlled dilution ratio of soap to water;
(b) at least one manifold connected to receive said pressurized aqueous solution;
(c) a plurality of nozzles mounted upon said manifold to uniformly distribute said pressurized liquid solution upon said mat and said belt, and
(4) means for hot pressing said mat to bind and shape said coated wood strands.
A feature of this invention is that the apparatus for distributing a release agent eliminates severe sticking of ligno-cellulosic material, coated with an organic polyisocyante binder, to the metal surface of the press plates and/or the steel mesh conveyor belts. Moreover, the even distribution of a controlled quantity of metallic soap prevents the undesirable discoloring of the surface of the final product. In addition, unlike wax release agents, the metallic soaps employed in this invention do not adhere and interfere with the moving parts of the wood product manufacturing equipment, thus reducing maintenance time and increasing product output.
Other objects, features and advantages will be readily apparent from the following detailed description of preferred embodiments thereof.